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In the context of the Chinese government's policy guidance, there is black soil protection and ecological environment protection. The purpose of this paper is to solve the problem that the soil ecology of the black soil in Northeast China is changing year by year, and it is necessary to explore the sowing and fertilization strategy under the new situation; most Chinese growers rely excessively on their personal experience in the process of soybean sowing and fertilization. In this study, we used "Heihe 43" soybeans and used regression experimental design methods to analyze the effects of planting density, nitrogen, phosphorus, and potassium fertilizer application on soybean yield and to determine the optimal planting density and fertilizer ratios. The study reveals that the optimal soybean planting density in Northeast China is 45.37 × 104 plants/ha, with nitrogen at 98.4 kg/ha, phosphorus at 218.96 kg/ha, and potash at 47.62 kg/ha. Under these conditions, soybean yields can reach 3816.67 kg/ha. This study can provide a theoretical method for decision-making to obtain the optimal planting density and fertilizer ratio for different regions of the farming system. [ABSTRACT FROM AUTHOR]

The aerodynamic roughness length (z0m) is an important parameter that affects the momentum and energy exchange between the earth surface's and the atmosphere. In this paper, the gradient wind speed data that were observed from May to October, 2014, at the Si Daoqiao station, which is located in an area of sparse Tamarix in the downstream region of the Heihe River Basin (HRB), are used to evaluate the sensitivity of the moderate-resolution imaging spectroradiometer (MODIS) near-infrared (NIR) bi-directional reflectance distribution function (BRDF) R, the MODIS/Landsat 8 normalized difference vegetation index (NDVI), and the wind speed at 5 m in comparison with the field-measured z0m. The results indicate that the NIR BRDF_R_MODIS and the NDVIMODIS/NDVILandsat8 are less sensitive indicators of the z0m over sparse Tamarix areas (R2: 0.0045 for NIR BRDF_RMODIS; R2: 0.0342 for NDVIMODIS; and, R2: 0.1646 for NDVILandsat8), which differs significantly from the results obtained by previous studies for farmlands and grasslands. However, there is a nearly linear correlation between the wind speed at 5 m and the z0m at the time scale of the NDVILandsat8 acquisitions (R2: 0.3696). Furthermore, the combination of the NDVI and wind speed at 5 m can significantly improve this correlation (R2: 0.7682 for NDVIMODIS; R2: 0.6304 for NDVILandsat8), whereas the combination of the NIR BRDF_RMODIS and wind speed at 5 m still has a low correlation (R2: 0.0886). Finally, the regional z0m of the oasis in the downstream region of the HRB was determined using Landsat 8 surface reflectance data and the wind speed data at the Si Daoqiao station, which properly reflect the temporal evolution of the z0m in that region. The parameterization scheme proposed in this paper has great potential to be applied to evapotranspiration, land surface, and hydrologic model simulations of sparse Tamarix at Si Daoqiao site in the future. [ABSTRACT FROM AUTHOR]

Net radiation is an important component of the earth's surface energy balance, which plays a vital role in the evolution of regional climate or climate change. The estimation of this component at regional or global scales is critical and challenging due to the sparse and limited ground-based observations. This paper made an attempt to analyze the feasibility of a remote sensing-based surface energy balance model using satellite (TERRA/MODIS) data to derive the net radiation (Rn). In the present study, MODIS data at 15 different days of the year (DOY) were utilized to visualize the spatial pattern of net radiation flux over three versatile and heterogeneous ecohydrological land surfaces (upstream, midstream, and downstream) of northwest China (Heihe river basin). The results revealed that the estimated net radiation from the satellite data agrees well with the ground-based measurements over three different surfaces, with a mean relative error of 9.33% over the upstream superstation (grasslands), 13.95% over the middle stream superstation (croplands), and 11.63% over the downstream superstation (mixed forests), where the overall relative error was 11.64% with an overall rmse of 29.36 W/m2 in the study area. The regional distribution of net radiation over the versatile land surfaces was validated well at a large scale during the five-month period and over different land surfaces. It was also observed that the spatial pattern of net radiation varies spatially over three different landscape regions during four different days of the year, which might be associated with different climatic conditions and landscape features in these regions. The overall findings of this study concluded that satellite-derived net radiation can rationally be obtained using a single-source remote sensing model over different land surfaces. [ABSTRACT FROM AUTHOR]

The aerodynamic roughness length (z0m) is a crucial parameter for reliably simulating turbulent exchanges between the land surface and the atmosphere. Due to the large number of input variables related to vegetation growth and aerodynamic conditions near the surface, estimating z0m precisely is difficult and, to date, no universal model has been established. Understanding the z0m changes in time series data and the relative contributions of vegetation indices and meteorological factors is important to providing a basis for modelling z0m. In this paper, the main meteorological factors that influence z0m in different seasons are presented based on data from three automatic weather stations (AWSs) that represent various land surface patterns in the Heihe river basin. A correlation analysis identified the dominant factors that influence z0m changes at half-hour and daily scales; then, a factor analysis was performed to identify the different contributions of vegetation indices and meteorological factors to z0m at different time scales. The results show that meteorological factors (wind speed, wind direction and atmospheric stability) are the main driving factors for z0m at the Arou and Guantan sites, which are situated in grassland and forest mountain areas, respectively, and that the vegetation indices have no impact on the z0m variations in these areas. In contrast, for the Daman site, situated in flat farmland, the vegetation indices are the primary driving factors, while meteorological factors such as wind speed and atmospheric stability are secondary factors, and wind direction has no significant influence. Finally, a detailed analysis was conducted to detect the relationships between half-hourly z0m measurements and three dominant meteorological factors. [ABSTRACT FROM AUTHOR]